1. Field of the Invention
The present invention relates to an active matrix substrate forming a display device such as a liquid crystal display device and an EL (electroluminescence) display device. More particularly, the present invention relates to a defect repair technology for an active matrix substrate.
2. Description of the Related Art
An active matrix substrate has been widely used in display devices such as a liquid crystal display device and an EL display device. For example, an active matrix substrate forming a liquid crystal display device is disclosed in Japanese Laid-Open Patent Publication No. 9-152625.
FIG. 14 is a plan view of a single pixel of a conventional active matrix substrate 120. This active matrix substrate 120 includes a plurality of pixel electrodes 112 arranged in a matrix pattern, TFTs (Thin Film Transistors) 105 respectively corresponding to the pixel electrodes 112, a plurality of gate lines 101 extending in parallel with each other between the pixel electrodes 112, a plurality of source lines 103 extending in parallel with each other between the pixel electrodes 112 in a direction crossing the extending direction of the gate lines 101, and capacitor lines 102 extending in parallel with each other between the gate lines 101.
Each TFT 105 includes a gate electrode 101a connected to a corresponding gate line 101, a semiconductor layer 104 covering the gate electrode 101a, a source electrode 103a formed over the semiconductor layer 104 and connected to a corresponding source line 103, and a drain electrode 103b facing the source electrode 103a over the semiconductor layer 104. The drain electrode 103b is extended to a region where a corresponding capacitor line 102 extends, so as to serve as an extended drain electrode 107 and a capacitor electrode 106. The extended drain electrode 107 and the capacitor electrode 106 are connected to a corresponding pixel electrode 112 through a contact hole 111b. 
In a liquid crystal display device (a liquid crystal display panel) including the active matrix substrate 120, a counter substrate having a common electrode, and a liquid crystal layer interposed between the active matrix substrate 120 and the counter substrate and including liquid crystal molecules, an image is displayed by transmitting as appropriate an image signal to the pixel electrodes 112 connected to the respective TFTs 105 by using a switching function of the TFTs 105. In the active matrix substrate 120, an auxiliary capacitor is formed between each capacitor line 102 and each capacitor electrode 106 in order to prevent self-discharge of the liquid crystal layer during an off-state period of the TFTs 105 or to prevent degradation of an image signal due to an off-state current of the TFTs 105, and for use as, for example, a path for applying various modulating signals for liquid crystal driving.
Recently, in order to implement a wider viewing angle, a VA (Vertical Alignment) mode liquid crystal display device having multi-domains, i.e., an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device, has been widely used in a large size liquid crystal television apparatus (liquid crystal TV) and the like (for example, see Japanese Laid-Open Patent Publication No. 2001-83523).
In such an MVA mode liquid crystal display device, an incision pattern (a slit portion) or a projection for controlling orientation of liquid crystal molecules is formed in pixel electrodes of an active matrix substrate and a common electrode of a counter substrate in order to form a fringe field. A wider viewing angle is implemented by distributing the orientation direction of the liquid crystal molecules in a plurality of directions by using the fringe field. Japanese Laid-Open Patent Publication No. 2001-117083 discloses a technology of embedding an electrode at a location corresponding to the incision pattern of the pixel electrode and the common electrode in order to prevent light leakage and to improve an initial response speed after voltage application.
In a manufacturing process of an active matrix substrate, foreign particles on the substrate or the like may cause gate line disconnection. A normal voltage (a drain voltage) cannot be applied to pixel electrodes on the disconnected gate line. Therefore, dot defects are visually recognized as a line defect along the disconnected gate line on the display screen of the liquid crystal display device. A liquid crystal display device becomes defective as the number of such line defects increases. As a result, manufacturing yield of the liquid crystal display device is reduced.
For example, Japanese Laid-Open Patent Publication No. 5-333373 discloses an active matrix liquid crystal display device having a repairing crossing portion in order to repair gate line disconnection. The repairing crossing portion is formed in the same layer as a capacitor line and has portion overlapping a pixel electrode and a source electrode.
However, a method for repairing a liquid crystal display device described in Japanese Laid-Open Patent Publication No. 5-333373 has the following problem: when disconnection is repaired, a pixel adjacent to a pixel corresponding to the disconnected location does not function normally, resulting in a pixel defect.